Mechanisms Associated to Third Generation Cephalosporin (TGC) Resistance in Enterobacteriaceae Isolated in Santa Fe, Argentina.

MARCHISIO MARTÍN; HANG ESTEFANÍA; RICO MARINA; JORIS ROMINA; ARGARAÑÁ FERNANDA; VACCARI MARÍA; MENDEZ EMILCE; BARONI MARÍA ROSA; MOLLERACH ANALIA; RADICE MARCELA; DI CONZA JOSÉ

Washington

Conferencia; 54th ICAAC - Annual Interscience Conference on Antimicrobial Agents and Chemotherapy; 2014

American Society of Microbiology

BACKGROUND Resistance rates to TGC and other antibiotics have been continuously increasing, within both nosocomial and community isolates, being the acquisition and expression of extended spectrum beta-lactamase (ESBL) of great concern. This study was conducted to estimate the TGC resistance prevalence in Enterobacteriaceae in Santa Fe city and to elucidate the mechanisms involved. METHODS All TGC resistant Enterobacteriaceae isolates (cefotaxime (CTX) and/or ceftazidime (CAZ)) obtained during two periods of 30 days from 4 health institutions were included in this study. Susceptibility profiles and phenotypic ESBL confirmation were evaluated by agar diffusion method following CLSI guidelines. The presence of AmpC beta-lactamases was analyzed by synergy test between TGC with phenylboronic acid. ESBL coding genes were invetigated by PCR. RESULTS From 675 Enterobacteriaceae isolates, 60 displayed TGC resistance, corresponding to 31 Klebsiella pneumoniae (52%), 16 Escherichia coli (27%), 6 Enterobacter spp. (10%), 5 Proteus spp. (8%) and 2 Serratia marcescens (3%). Forty nine of 60 isolates were characterized as ESBL producers, while 8/60 and 3/60 as AmpC and KPC carriers, respectively. Twenty one isolates produced CTX-M-1 group β-lactamases (17 K. pneumoniae, 3 E. coli and 1 Enterobacter sp.), 14 produced CTX-M-2 group enzymes (7 K. pneumoniae, 5 E. coli and 2 P. mirabilis), 5 corresponded to CTX-M-9 group (4 E. coli and 1 K. pneumoniae), 1 to CTX-M-8/25 groups (1 K. pneumoniae) and 10 to PER-2 (5 K. pneumoniae, 2 S. marcescens, 1 E. coli, 1 Enterobacter sp. and 1 P. mirabilis). Two K. pneumoniae co-produced CTX-M and PER-2 beta-lactamases. CONCLUSIONS Cefotaximases belonging to four genetically different groups constitute the main TGC resistance mechanism in enterobacteria in our region. K. pneumoniae was the most prevalent species displaying TGC resistance and CTX-M-1 group constitutes the most prevalent resistance determinant while CTX-M-2 and -9 groups were the common amongst E. coli.